1. Field of Invention
The present invention relates to a sealing material for solid oxide fuel cells, especially for a sealing material, which can harden quickly at a room temperature without a baking step, for solid oxide fuel cells.
2. Related Art
A solid oxide fuel cell (SOFC) is expected as one of the best prospect green energy in this century, and it has several characteristics of high efficiency, friendly for the environment, quiet, and good reliability, etc. Compared to tubular and mono-block layer built (MOLB) type solid oxide fuel cells, a planar solid oxide fuel cell has benefits of short current flow path, uniform collection, and high power density of cells. Therefore, the planar solid oxide fuel cell is always a main object of solid oxide fuel cells to be researched and developed.
Since there are a fuel gas (hydrogen, anode) and an oxidation gas (oxygen, cathode) existing around both sides of an electrolyte while the planar solid oxide fuel cell is working, a sealing material is needed to separate anode and cathode working chambers and provide sealing performance. In a sealing process, the sealing material should be fully soaked and adhered with the bipolar plates and the electrolyte to achieve the sealing performance. Meanwhile, the sealing material and the materials contacting with it should keep thermal matching, chemical stability, dimensional stability, and electrical isolation in an oxidation reduction atmospheres to guarantee the sealing performance could be kept for a long time. Because of the strict requirement of performance, finding appropriate sealing materials is always a tough technological point for developing the planar solid oxide fuel cell.
It is a trend to develop intermediate temperature (600° C. to 850° C.) planar solid oxide fuel cells. There are many reports about nucleated glass utilized in high temperature (1000° C.) solid oxide fuel cells for sealing before. However, there are still short of reports about sealing materials for the intermediate temperature planar solid oxide fuel cells.
For the intermediate temperature planar solid oxide fuel cell adopting metal bipolar plates, low melting glass is usually chosen as a sealing material. Besides silicon, the glass is composed of a large quantity of alkaline metal oxide and alkaline earth metal oxide. These compositions would move in a fuel cell system easily and react with other fuel cell components. Therefore, for the planar solid oxide fuel cells, technical researchers do a lot of job to develop the sealing materials which can match these fuel cell components. Research works are focused on alkaline metal silicates, alkaline earth metal silicates, alkaline metal boron silicate glass, or glass-ceramics such as Pyrex glass and aluminum phosphates. Nevertheless, various materials have defects that thermal expansion coefficients do not match and stabilities for long term operation are poor for example.
Therefore, the inventors of the present invention design a sealing material for fuel cells to solve the above problems.